I guess their inventory is gone. To my knowledge there is no other current source for new reproduced lifters so I perhaps it's repair what you have or buy some used ones? I know Kanter has the equipment to test the lifters, I've inquired to them as to what they can offer you, and I'll advise when I hear back from Fred or Dan.

UPDATE. I spoke with Fred Kanter. Their current stock of reproduction 356 lifters has sold out and the minimum order quantity for a new production run far exceeds the available market for them. Looks like finding good used units is your only option at this point unless you can find someone who bought them but never used them.